Monolithic circuits, such as semiconductors, piezoelectric devices, ceramic filters, and the like, often require diverse materials to reside in diverse areas of a common substrate. Conventional thin film patterning, depositing, and etching techniques may be employed to successfully position the diverse materials at diverse areas of a substrate.
While these conventional techniques work well, they are occasionally unduly complex and expensive. For example, protective layers must often be applied in predetermined patterns to protect against unwanted etching. After etching, the protective layers must then be removed. Moreover, when several different materials are involved, separate etching steps may be required for each material. Consequently, if a material or several different materials can be applied using a process that does not require etching, significant savings may be obtained over the conventional thin film patterning, depositing, and etching techniques.
A conventional shadow masking process need not require etching steps. A shadow mask is a stencil. In a conventional shadow masking process, a mask is prepared in which a pattern to be formed represents an open or void area through the mask. A thin film deposition process may be used to deposit a material through the open area of the mask. Areas where a material is not to be applied are blocked by solid portions of the mask. Material is applied to a substrate only where permitted by the shadow mask, and etching steps are not required. On the other hand, conventional shadow masking processes do not work for all types of patterns.
In particular, conventional shadow masks do not support continuous ring, spiral, and like patterns. These patterns require the mask to include an open portion that, for the most part, surrounds a solid portion. The mask cannot mechanically hold the surrounded solid portion inside the open portion without running a solid "land" region across the open portion. When the pattern is a sealing ring to which a cap will attach to hermetically seal the monolithic circuit, the solid land region would produce a discontinuity or void in the sealing ring that would spoil any hermetic seal.
Thick film deposition techniques have been used to form continuous ring, spiral, and like patterns. Thick film techniques form a mask with open and solid areas on a screen. A viscous liquid material is then forced through the screen in open areas of the mask. The material may then flow together under the screen to smooth out any discontinuities caused by the screen. Thus, a continuous pattern may result. Unfortunately, the requirement for a liquid-like material makes this technique unworkable in many situations. The flowable nature of the material can require such high temperatures that the substrate and/or any prior processing on the substrate become damaged. Moreover, the flowable nature of the material often prevents high resolution patterning.